The present invention relates to an information processing system including a plurality of network-connected storage systems, and a data transfer technology.
In an information processing system including a storage system, if any failure occurs to the information processing system due to natural disaster exemplified by earthquakes or hurricanes, or power failure, data in the storage system may entirely or partially lost. Also, operations utilizing the information processing system may be stopped. As a possible solution for such problems, a storage system (hereinafter, referred to as destination storage system) is placed at some distance from another storage system that is in charge of operations (hereinafter, referred to as source storage system) so that data is to be written into both the source and destination storage systems. Such a dual-writing technology is referred to as remote copy.
The remote copy is classified into two modes of synchronous remote copy and asynchronous remote copy.
In the synchronous remote copy, every time a write request is issued to the source storage system, data is responsively written to both the source and destination storage systems. After such data dual-writing, an acknowledgment of write is issued. In such synchronous remote copy, the high identicalness of data is achieved between the source and destination storage systems. Accordingly, even if a failure occurs to the source storage system, consequential data loss can be minimized. There is a drawback, however, of lengthening a write response time with an increase of the distance between the source and destination storage systems.
In the asynchronous remote copy, when a write request is issued to the source storage system, the source storage system is responsively written with data. After such data writing, an acknowledgment of write is forwarded back to the source of the write request, and then the data is copied from the source storage system to the destination storage system. As such, the write response time is shorter compared with the synchronous remote copy. There also is a drawback, however, of easier and larger amount of data loss if a failure occurs to the source storage system compared with the synchronous remote copy.
The remote copy is defined to be applied between any arbitrary storage areas in a storage system. This is referred to as remote copy pair.
As to data transfer in the asynchronous remote copy, Patent Document 1 (JP-A-H11-85408) describes the technology of assuring the data-write-sequence consistency in a destination storage system as well as in a source storage system. In Patent Document 1, when a write request is accepted in the source storage system, data for writing is added with control information indicating the data writing sequence. Utilizing such control information, the destination storage system sorts the writing data transferred by the source storage system. The resulting writing data is then reflectively stored into the destination storage system in the sequence of data writing.
Patent Document 1 also describes the asynchronous remote copy between a primary site and a secondary site. The primary site includes a plurality of source storage systems, and a primary host computer (in the below, referred to as primary host) that makes accesses to these source storage systems. The secondary site includes a plurality of destination storage systems, and a secondary host computer (in the below, referred to as secondary host) that makes accesses to these destination storage systems. As such, in Patent Document 1, the technology of assuring the data-write-sequence consistency is also applicable to a case where the source and destination storage systems are each provided plurally.